What are some sad things in the world that most people are unaware about?

This is the now extinct Kauaʻi ʻōʻō Bird.

There is a recording of the last surviving member singing a love song out to a mate that could never be responded to (I’ll include a link in the comments).

It’s extremely sad because you know that would be the last of its kind. The species lived on the island of Kauai and went extinct because of the introduction of invasive species and because of mosquito borne diseases. Sadly, this is the story of many species. There are final acts and moments, but this is the rare case where it is well documented.

The saddest part of the final Kauaʻi ʻōʻō song is that there are pauses in it as the male waits for the female to respond, but that response never comes. He passed away in 1987.